1. Field
The invention relates generally to apparatuses for determining whether a substance is carried in a fluid.
2. Related Art
In some circumstances, it may be desirable to determine whether a substance is carried in a fluid. For example, various pathogens may be present in water intended for human consumption, and determining whether such pathogens are present in such water may advantageously prevent consumption of such pathogens and thus prevent waterborne disease.
One method for determining whether pathogens are present in water involves measuring turbidity of the water. However, turbidity may indicate substances other than pathogens, and also pathogens may be present in relatively clear water. Therefore, measuring turbidity of water may be an unreliable method for determining whether pathogens are present in the water.
Another method for determining whether pathogens are present in water involves measuring a quantity of coliform bacteria in the water. Coliform bacteria are naturally present in the digestive tracts of many animals, and therefore may indicate fecal contamination in the water. However, coliform bacteria in the water may not reveal some other pathogens in the water, and measuring a quantity of coliform bacteria may require 24 to 48 hours, for example, for growth of the coliform bacteria to a measurable quantity.
Another method for determining whether protozoan pathogens (such as Cryptosporidium parvum or Giardia lamblia, for example) are present in water involves filtering the water and examining the filter for such pathogens. However, filtering water may not reveal smaller pathogens, and examining a filter for protozoan pathogens may require time-consuming laboratory analysis.
Another method for determining whether pathogens are present in water involves passing the water over a plurality of beads having capture surfaces configured to capture the pathogens. An apparatus including such a plurality of beads may be referred to as a “packed bed” apparatus. However, in such an apparatus, the spaces between the surfaces of the beads are inconsistent. In some regions, the space between adjacent beads may be so small that water flow on such regions is unduly restricted. In other regions, the space between adjacent beads may be so large that some pathogens in the water pass between the adjacent beads sufficiently far from the capture surfaces that the pathogens escape capture. Such inconsistent spacing may therefore decrease efficiency of such a packed bed apparatus.